"I thought I would try something different."
This doesn't usually go well! Here are two examples:
[Event "Exeter Juniors vs Sidmouth"] [Site "?"] [Date "2012.04.28"] [Round "2"] [White "Warburton, Ralph"] [Black "Royle, James"] [Result "1-0"] [ECO "A60"] [PlyCount "49"] 1. d4 e6 2. c4 c5 3. d5 Nf6 4. Nc3 d6 5. Bg5 h6 6. Bh4 b6 7. e4 Bb7 8. Be2 Nbd7 9. Nf3 g5 10. Bg3 Nh5 11. O-O Nxg3 12. fxg3 Nf6 13. e5 dxe5 14. Nxe5 exd5 15. Qa4+ Ke7 16. Rae1 Qd6 17. Bf3 Ne4 18. Nxf7 Kxf7 19. Bxe4+ Ke7 20. Bxd5+ Kd8 21. Bxb7 Rb8 22. Re8+ Kc7 23. Rf7+ Be7 24. Rfxe7+ Qxe7 25. Qc6# 1-0
[Event "Exeter Juniors vs Tiverton"] [Site "?"] [Date "2012.05.02"] [Round "2"] [White "Trott, Tomas"] [Black "Thorpe-Tracey, Stephen"] [Result "0-1"] [ECO "B07"] [PlyCount "52"] 1. d4 Nf6 2. Nc3 g6 3. g3 Bg7 4. Bg2 O-O 5. e4 d6 6. Bf4 Nbd7 7. Nf3 c5 8. e5 dxe5 9. Nxe5 cxd4 10. Nd5 Nxd5 11. Nxf7 Rxf7 12. Bxd5 e6 13. Bxe6 Qe8 14. Qe2 Nc5 15. Bxf7+ Qxf7 16. O-O Bf5 17. Rfd1 Rd8 18. c3 d3 19. Qe3 b6 20. f3 Qd5 21. g4 Bc8 22. Bg5 Rf8 23. Bf4 Ba6 24. a3 Ne6 25. Bg3 Rxf3 26. Qd2 Ng5 0-1
After 1.e4, I expect Tomas has a fair idea about what to do and what sort of position he is aiming for. After 1.d4, is that really still true? It is definitely still true for Tomas' opponent, who I expect plays those first few moves in every game. Black didn't really have to think until move 7, when White was already losing at least a pawn.
The moves White played weren't daft, but he didn't seem to know what he was doing or what the usual tricks are in those sorts of positions. The game was a fairly easy win for Black and White didn't really have any chances at all to draw, let alone win.
Same thing in James' game last time. I know I have given James a book which says, play 1...e6 and 2...d5. James chose something else, not anything daft, because he's not daft, but he didn't know what to do. He ended up failing in all three of the very basic opening goals: get your pieces out, get at least a stake in the centre, and get castled.
The Benoni is actually a reasonable defence to 1.d4, but Black didn't know that, and didn't know what the right plans are in those sorts of positions. And by the look of it, White had seen it all before, and knew exactly what to do about it: put all the pieces in the middle and blast through with e4-e5.
So, no more of this, please! Pick an opening, learn it, and stick to it!
When you sit down to play, you really must have four systems in your head: 1. what to play as White as your main opening system 2. what to do if Black dodges 3. what to play as Black against 1.e4 4. what to play as Black against 1.d4
I think I've given you all a booklet with enough to get started on all four systems (different systems for each of you). Please read! I'd hate for it to feel like homework, but I also hate watching you suffer in the opening against experienced players.
Now, you may always find an opponent who knows more about the opening than you do. That doesn't mean the best thing to do about it is to play something different than usual, which you don't know anything about! This is especially true if you are playing an experienced player. They may have been playing chess long enough to have played, or played against, almost every opening there is, and will know much more about what to do.
What you have to do is be an expert in your opening, so that even if you do get a surprise, you have an idea about what sorts of things there are to do for your side.
If you want to try something different: 1. Pick something different from a list of known systems 2. Read a bit about it 3. Try it out in friendly games first to get the hang of it 4. Then you can spring it on an opponent in a match!